Nowadays, the use of mobile devices, e.g. personal digital assistants, portable computers and mobile phones, for wireless communication purposes is widespread. Furthermore, new applications for these devices are rapidly emerging. In many of these new applications, services are provided which relate to functionality to the end user of the mobile device based on its location, so called Location Based Services (LBS). Such services include for example providing navigational support, providing a local weather forecast or searching for a nearby restaurant.
Depending on the type of service to be provided, different methods of determining the location of the mobile device can be applied. Some services require very accurate locations, while others only need to know the location in a more general fashion.
Well-known methods of determining the location of a mobile device are based on the location of a base station of the radio cell the mobile device is camped on. In these methods, localization may for example be based on cellular base station identifiers sent by cellular base stations in the network. If the mobile device knows the geographic location of the base stations corresponding to the base station identifiers, it can determine its position. The determination may be done by assuming that the position of the mobile device coincides with the closest base station, by calculating the position using a triangulation technique based on positions of surrounding base stations, or by using other techniques known to a person skilled in the art.
Because the coverage area of a cellular base station is relatively large, the accuracy of the localization will be relatively low. This may become an issue for future mobile device applications, in particular if these applications involve LBS that need a very accurate location determination. Especially in buildings, the location determination can be improved, e.g. to determine on which floor the mobile device is located.
One way to improve the accuracy of the determined position is to base the location determination on wireless access points, e.g. access points used in a wireless local area network (WLAN). Wireless access points generally have a smaller coverage area than cellular base stations. Furthermore, wireless access points are often located in buildings. By using access point identifiers, Service Set Identifier (SSID) in WLAN, a more precise location determination is possible. A method of determining a location of a mobile device based on wireless access points is described in U.S. Pat. No. 6,968,194. A wireless access point that is equipped to be used in such a method has for example been described in European patent application 1802154.
In order to perform a location determination based on access point identifiers, an accurate location of the wireless access points themselves is needed. Unlike cellular base stations, wireless access points are often installed by the general public, not specifically skilled in operating (wireless) communication technology. As a result, a person may install a wireless access point without knowing how to assign a correct address or may forget to change the location of the wireless access point after moving the wireless access point to a new location. A three-point location determination based on three wireless access points, also referred to as triangulation, of which one access point has an inaccurate or incorrect address, will result in an erroneous location of the mobile device.